The Origins of Intellect

1
Introduction
Despite the clear implication of its title, this chapter is not the beginning of the book. It begins on see here in the Preface to the First Edition.
It is true that a preface always contains some information that is of no interest to most readers, but the Preface is more important in this book than in most. It explains the structure of the book, and that structure is essential to efficient study of the main body of the text.
PIAGET AND HIS METHODS
Jean Piagetb is a Swiss psychologist who was trained in zoology and whose major interests are essentially philosophical. He and his associates have been publishing their findings on the development of cognitive processes in children since 1927, and haveaccumulated the largest store of factual and theoretical observations extant today.
Piaget is often criticized because his method of investigation, though somewhat modified in recent years, is still largely clinical. He observes the child's surroundings and his behavior, formulates a hypothesis concerning the structure that underlies and includes them both, and then tests that hypothesis by altering the surroundings slightly--by rearranging the materials, by posing the problem in a different way, or even by overtly suggesting to the subject a response different from the one predicted by the theory.
An example of the method is the investigation of the preoperational child's conception of velocity. The child observes the movement of an object through points A, B, C, and D. He reports that the object passed through point D "after" point A and that it took "more time" to get from A to C than from A to B. From this it might reasonably be inferred that the child's conception of temporal succession and duration is the same as that of an adult. But the investigation doesn't stop there. The subject is then presented with the simultaneous movements of two objects. The investigator systematically varies the actual distance through which each of the objects moves, their times in transit, and their initial and terminal positions relative to one another. When that is done, the child no longer responds as an adult would in similar circumstances. For example, if two objects move simultaneously--i. e., if they start simultaneously and stop simultaneously--but at different velocities, the child will deny their simultaneity of movement. To him, each moving object has a different "time"--a time that is a function of the spatial features of the display.
The systematic manipulation of variables illustrated by that example is certainly in the tradition of classical experimentalscience. The example, however, is drawn from one of the more rigorous of the studies done by Piaget and his colleagues. Their investigations often begin with naturalistic observations and continue as an interaction between the child and the "experimenter" --an interaction in which each varies his own behavior in response to that of the other.
Another example may serve to illustrate the point: it is an "experiment" designed to reveal the child's conception of number. The child is presented with an assemblage of coins and a large number of flowers; he is asked to tell how many flowers he can purchase with the coins if the price of each flower is one coin. Here is a transcript of one such encounter:
Gui (four years, four months) put 5 flowers opposite 6 pennies, then made a one-for-one exchange of 6 pennies for 6 flowers (taking the extra flower from the reserve supply). The pennies were in a row and the flowers bunched together: "What have we done?--We've exchanged them.--Then is there the same number of flowers and pennies?--No.--Are there more on one side?--Yes.--Where?--There (pennies). (The exchange was again made, but this time the pennies were put in a pile and the flowers in a row.) Is there the same number of flowers and pennies?--No.--Where are there more?--Here (flowers).--And here (pennies)?--Less.1
This shifting of experimental procedures to fit the responses of a particular subject makes replication difficult, and the results may be especially susceptible to the "experimenter effect."* The reader who feels impelled to criticize Piaget's method is in good company. But before becoming too enthusiastic a critic, he should be sure to note the deliberate effort that is made to give
*Sometimes called the "Rosenthal effect," after R. Rosenthal, who in several recent studies has demonstrated that even in apparently objective experimental situations, the experimenter can influence the subject's behavior in a number of subtle and unacknowledged ways (facial expression, tone of voice, etc.). Even rat subjects perform better for experimenters who expect them to do so, presumably because of differences in handling by different experimenters. 3
the child opportunities for responses that would not fit the theory. He should also keep in mind Piaget's epistemological position that knowledge is action (though not necessarily motor action). The subject is continually acting. His actions are structured, and they are also to some extent autonomous. The investigator must therefore continually change his line of attack if he is to follow those actions and to discern their underlying structure. Indeed, since that structure does differ from child to child, the investigator may find it necessary at times to vary his language when posing a problem in order to ensure that the problem will be the same for different children. Rigidly standardized procedures might defeat the very purpose for which they were designed, because their meanings vary from one subject to another. The important thing is to "make contact with the child's thinking."2
RELATION TO AMERICAN PSYCHOLOGY
The early work of Piaget's Geneva group was given considerable attention in the scholarly press, but because psychology, especially in the United States, was at that time dominated by associationistic theories of learning and by content-oriented psychometrics, their work generated little interest.
The current explosion of interest in Piaget's work is an expression of the same concern that has produced conceptions of man as a rule-formulating, rule-following organism and of his brain as an incredibly complex organic system for processing information. That concern may have resulted not only from a dissatisfaction with existing theories but also from advances that have taken place recently in neurophysiology and computer engineering.
In any case, Piaget's observations and formulations are today a definite focus of theoretical and professional interest in psychology. The theory is cognitive rather than associationistic, c itis concerned primarily with structure rather than content--with how the mind works rather than with what it does. It is concerned more with understanding than with prediction and control of behavior.
These remarks can of course be made only by way of emphasis, for we can never know the how except through the what; we can only infer central processes from the behaviors that they organize. An affirmation of one kind of analysis does not necessarily imply a negation of the other. There are conflicts between them, but often the dissonance is more apparent than real, and a careful reading of both kinds of analysis reveals a harmony that could not be seen at first glance. In this book, discussion of Piaget's theory is written only partly in the idiom of Piaget. "Input," "output," and "feedback," for example, are less-than-lyrical words that American psychologists have borrowed from engineering. Piaget does without them, but we shall find them useful. Even the term "learning" appears very seldom in Piaget's writings, and when it does, it is nearly always accompanied by a modifier. Conditioning, whether classical or instrumental, respondent or operant, he calls "learning in the narrow sense"; changes in cognitive structure are referred to not as learning but as "development." In this book, we shall use both the Piagetian and the more standard psychological terms and attempt to understand how they all relate to Piaget's ideas.
One more thing should be said about his system in relation to others. Piaget's early academic training was in zoology, and his theory of cognitive development is rooted firmly there. That, coupled with the feature of invariant stages, has caused some writers to label the theory "nativist," as though it were holding the child's genetic program responsible for the organization ofhis behavior. But Piaget's is not a nativist theory. A radical alternative to nativism is "empiricism," the doctrine that behavior is determined by the environment--by reinforcement contingencies and the like. But the theory is not empiricist, either. It has properly been called "interactionist" and "constructivist": the organism inherits a genetic program that gradually (through a process called "maturation") provides the biological equipment necessary for constructing a stable internal structure out of its experiences with its environment. Paradoxically, that stable structure--that "intelligence"--then helps the organism adapt to changes in that environment. Our discussions of assimilation, accommodation, and equilibration will attempt to resolve the paradox.
Before turning to the first of the Piagetian periods of development, let us take a quick overview of the theory, in preparation for the more detailed account that will follow in Chapters 2 through 5.
EVOLUTIONARY PERSPECTIVE
The evolution of complex organisms has necessarily been accompanied by that of complex behavioral control systems. A one-celled animal reacts in a severely limited way to its immediate environment; a higher animal has an elaborate repertory of responses to a wide variety of stimuli. But that elaboration and that flexibility are achieved at the expense of biological simplicity; such an animal is composed of many parts--some specialized for reception of information from the environment, others for actions upon it. If it is to adapt successfully to its environment, the higher animal, therefore, must possess a transmission device that integrates the activities of the parts. And of course if it is to survive, the animal must adapt.
But once a transmission system has developed, the way is open to the development of alternative arrangements of that system. Thus, not only are the higher animal's reception and responsecapabilities complex, but so are the mechanisms that relate those capabilities; relations between stimulus and response are different for higher and lower animals. A lower animal is "sense-dominated"; its response to a specific input from the environment is immediate and predictable. A higher animal's behavior, however, is controlled not only by inputs from its immediate surroundings, but also by mediating processes within the transmission system--processes that are partly the result of previous functioning of the system. Therefore, the higher animal's overt response to a specific input is not necessarily immediate, and it is not predictable merely from knowledge of the current input pattern. To predict the behavior of a higher animal, it is necessary to know something about its mediating processes. In order to predict a human subject's response to a combination of digits--say "8" and "2"--I would have to know what he had learned about arithmetic before he ever came into my laboratory; whether he had in the immediate past been instructed to add, to subtract, to multiply, or to divide; whether he had a generalized set to follow directions; and so on. A person's behavior is determined both by the sensory input at the moment and by the way in which his system of mediating processes has been organized.4
The twin consequences of sensory and motor differentiations and of the organization of mediating processes are (1) the extension--both spatially and temporally--of the world with which the organism can interact and (2) the freedom to choose from among many possible actions. "Intelligence" is the ability to make adaptive choices.
STRUCTURE AND FUNCTION
Adaptation is a biological function. As a child develops, functions remain invariant, but structures change systematically. Change in structures is "development."
Another term found often in Piaget's writings is content, by which he means observable stimuli and responses. We may talkin abstract terms about "function" and "structure," but as soon as we cite an actual example, we must deal also with content.
Such an example might be: "A baby looks at a rattle and picks it up." The structure of that event relates the means (looking, reaching, grasping) to the end (stimulation from the object in hand). Each of those is related thereby to the other, and it is that relatedness that Piaget calls "structure."d The function of the baby's act is adaptation--i.e., the assimilation of inputs and the accommodation of each element to the others. "Content" refers to the input and output--the raw data of the event, as distinguished from its pattern. The term "structure," on the other hand, refers to the systemic properties of an event; it encompasses all aspects of an act, both internal and external.
Finally, "function" refers to biologically inherited modes of interacting with the environment--modes that are characteristic of such integrations in all biological systems. With reference to intelligence, that inherited "functional nucleus" imposes "certain necessary and irreducible conditions"5 on structures. Discontinuities in structure arise out of the continuous action of invariant functions. Throughout the developmental period, functions are permanent, but structures are transitory; if they weren't, there would be no development.
There are two basic functions: adaptation ("the accord of thought with things"6 ) and organization ("the accord of thought with itself"7). Adaptation, in turn, consists of assimilation and accommodation.
ASSIMILATION
If we think of the human brain as an organic machine for processing information, we must realize not only that it is an exceedingly complex machine, but also that its internal structure is continually changing. We must realize also that the precise pattern of cortical activity initiated by an incoming stimulus is afunction not only of the pattern of the stimulus, but also of the way in which the brain has been programmed to deal with it.
Assimilation occurs whenever an organism utilizes something from its environment and incorporates it. A biological example would be the ingestion of food. The food is changed in the process, and so is the organism. Psychological processes are similar in that the pattern in the stimulation is changed and, again, so is the organism.
In introductory psychology courses it is demonstrated that even the perception of an object is not a faithful reproduction of a stimulus pattern. For example, our perception of an object remains the same even though changes in distance, angle of view, and amount of light produce rather striking differences in the size, shape, brightness, and hue of the image that is actually projected onto the retina. (This is, of course, the phenomenon known as "object constancy.") Beyond that, objects are invested with meaning--i.e., they are categorized in terms of such dimensions as familiarity, threat, and beauty. In sum, the input is changed to fit the existing structures. The organism is always active, and its cognitions--even its perceptions of its immediate surroundings--are as much a function of that activity as they are of the physical properties of the environment.
ACCOMMODATION
But at the same time that the input is being changed by the structures, the mediating processes are being changed by the input. For example, object constancy, which was just used to illustrate the former, can also be used to illustrate the latter. Each "correction" that is applied by the brain to a retinal image had to be learned--i.e., the structures that act upon the input have themselves been shaped by that input.
Take size constancy, for example. Think of the thousands upon thousands of times that the size of an image on your own retina has covaried with distance from you to the object. Many other inputs, such as proprioceptive ones that arise as you have approached the object, and the temporal relations among them,have contributed to the changing patterns of mediation. e The mechanism by which those changes occur Piaget calls "accommodation."
FUNCTIONAL INVARIANTS: ASSIMILATION AND ACCOMMODATION
Accommodation and assimilation are called "functional invariants" because they are characteristic of all biological systems, regardless of the varying contents of those systems. They are not, however, always in balance, one with the other.
Temporary imbalances occur when a child is imitating (accommodation over assimilation) and when he is playing (assimilation over accommodation). Behavior is most adaptive when accommodation and assimilation are in balance; but such a balance is always temporary, because the process of adaptation reveals imperfections in the system. (See the section below on Equilibration.)
SCHEMES
As I mentioned previously, cognitive development consists of a succession of changes, and the changes are structural.
Piaget often refers to individual structures as schemes. A scheme is a kind of mini-system; it is that property of an action which can be generalized to other contents. For example, the baby who "looks at a rattle and picks it up" (see here) can do the same with any small, lightweight object; i.e., the "look-and-pickup" scheme can assimilate a wide variety of objects--with some accommodations, of course.
Actually, a scheme includes also the stimuli that trigger the mediating processes and the overt behavior that presumably isorganized by them. And there can be interactions among schemes; i.e., they can assimilate each other. A "scheme" is a generic unit of structure; "whatever is repeatable or generalizable" is a scheme.9 The earliest structures are relatively simple; they usually are referred to as "reflexes." Later schemes are more complex--more "mental"--and it becomes increasingly appropriate to think of them as "strategies," "plans," "transformation rules," "expectancies," etc. Whatever their labels, they form a kind of framework onto which incoming sensory data can fit--indeed must fit if they are to have any effect; but it is a framework that is continually changing its shape so that as many data as possible will fit.
Figure 1.1 summarizes some of these relationships.

RELATIONS AMONG CONCEPTS
Figure 1.1 is an attempt to represent the relationships among function, organization, adaptation, accommodation, assimilation, structure, and scheme. It will not be a successful attempt, however, if the diagram is conceived as an ordinary classification hierarchy in which, at any given level, each category is a viable entity unto itself. Having divided a deck of cards into spades, hearts, diamonds, and clubs, you can throw away all the hearts, say, or all the clubs, without affecting the contents of the remaining categories; those categories still exist, and in the same form as before. But without assimilation, there can be no accommodation; and accommodation is a change in structure, the function of which is to make possible the assimilation of some stimulus pattern that is not entirely familiar. Similarly, unless adaptation is organized, it is not adaptive. Furthermore, the structures that in the diagram are separate from functions are really ways of functioning--the enduring results of organizing adaptation (or adaptive organizing).
This attempt at extensive qualification of the apparently simple relations depicted in Figure 1.1 may be confusing, but it should serve to emphasize one of the salient features of Piaget's theory: its holism. The various entities in the diagram actually represent different aspects of a single entity: a functioning cognitive system.
EQUILIBRATION
One concept that is not represented by the diagram is that of equilibration. The word will not be used often in this book, but the idea to which it refers should be kept constantly in mind while studying Piaget's theory in subsequent chapters, for it was the inspiration for the theory in the first place and remains its overarching principle.
Equilibration is a function of every living system. It is a process of attaining equilibrium between external intrusions andthe activities of the organism. From a psychological point of view, those activities may be conceived as strategies for maximizing gains of information and minimizing losses.10 Equilibration is a mechanism of change that operates over an extended period of time in a developing child. To place it in proper perspective, it should be compared to another such mechanism: learning.
Behaviorists think of learning as the formation of associations. A response occurs in the presence of a stimulus, and a bond is formed such that henceforth when that stimulus is presented, that response will occur. Often there is an added requirement that the response be followed immediately by a special kind of stimulus called a reinforcer.
Although Piaget does not deny that such learning occurs, he has concluded that the fundamental process in learning is not association. He calls association "learning in the narrow sense," and is not much interested in it. What does interest him is a complex that includes maturation and a different kind of learning--a complex that he calls "development."
Possibly the most important difference between Piaget's developmental theory and traditional learning theory is that in addition to the gradual accretion of functional associations (isolated simple structures), Piaget's theory recognizes an intermittent revision of established structures--a process that entails qualitative as well as quantitative change. The process by which structures are revised is called equilibration.
Equilibration is "coming into equilibrium." In classical physics, there are two kinds of equilibrium: static and dynamic. A balance scale with equal weights in the two pans is a system in static equilibrium, as indeed is any body at rest. A thermostat is in dynamic equilibrium; so is a homeostatic biological system, a falling body after its acceleration has ceased, or any other system in which an interchange of forces maintains the system in a constant state. In Piaget's theory, equilibrium is dynamic; it is a system of compensating actions that maintain a steady state. That steady state is a condition of the system in which the internal activities of the organism completely compensate for intrusionsfrom without. Because of the importance of states (stages) in his theory, Piaget has often seemed uninterested in mechanisms of transition from one state to another; but the concept of equilibration is concerned with just those transitions.
An example is the acquisition of conservation of continuous quantity. The subject is presented with two identical beakers that have been filled to exactly the same level with fruit juice; one is identified as his, the other as the experimenter's. After the child has acknowledged that the amount of juice is the same in each jar, the experimenter pours the contents of one jar into a short, broad container and that of the other into a tall, thin one.
"Now," he says to the child, "Do you have more to drink, or do I, or do we have the same amount?" If the answer is "same amount," the subject is said to have "conserved" the substance of the liquid. With respect to this problem, at least, his thinking is "equilibrated."
According to Piaget, this, like all equilibration processes, goes through four steps.11 In Step 1, the subject attends to only one dimension (usually the height), and he judges the tall drink to be the larger; i.e., he fails to "conserve" quantity. Repeated experiences with configurations that are similar but not identical, however (liquids poured into vessels of varying shapes, fromvessel to vessel, etc.), eventually lead him to shift to the other dimension (in this case width). That shift is especially likely when the tall drink is constricted into a mere tube, for then its extreme thinness can hardly escape his attention, and he does indeed state that the tall drink is now the smaller of the two. "Focusing on the other dimension" is the second of the four steps of equilibration. The third step is a mixture of the first two--or rather, it is an alternation between them as the conditions of the display are changed. But that alternation, especially if it is rapid, provides the necessary conditions of the fourth step, which is simultaneous attention to both height and width and their coordination into a mutually compensating system. Now when he is asked, "Which has more to drink?" he replies firmly "They are the same."
In summary, a child approaches any conservation problem with a strategy for obtaining information from it. But the more consistently he applies that strategy (Step 1), the clearer it becomes to him that it is inadequate; so he shifts to another strategy (Step 2). When the second strategy also fails, he vacillates between the first two (Step 3), which results eventually in a stable system (Step 4) that modifies each and includes both. Now he has information not only about changes in one dimension (e.g., the height of a body of liquid) or about changes in another (e.g., its width), but about both of those plus conservation of whatever remains the same (e.g., the quantity of the liquid) throughout all those changes. The last strategy will not itself disintegrate; but it does contribute to further change, for its very stability makes possible an awareness of inadequacies in larger systems of which it is a part.
Structures continually move toward equilibrium, and when a state of relative equilibrium has been attained, a structure is sharper, more clearly delineated, than it had been previously. But the very sharpness points up inconsistencies and gaps in the structure that had never been salient before. Each equilibrium state therefore carries with it the seeds of its own destruction, for the child's activities are thenceforth directed toward reducing those inconsistencies and closing those gaps. Equilibrium is always dynamic and is never absolute, but the product of each ofthe major units of development (Sensorimotor, Concrete Operations, and Formal Operations) is a relatively equilibrated system of actions--an equilibrium.
FACTORS IN DEVELOPMENT
Equilibration is not the only factor in the intellectual development of a child (though it is the most important). Altogether, there are five: * maturation, physical experience, logico-mathematical experience, social transmission, and equilibration.
MATURATION
To some psychologists, maturation is simply [?] the process of attaining maturity, whatever the nature of that process might be. Piaget uses the term more specifically to refer to a gradually unfolding genetic plan. Genetic effects are never seen in isolation, of course; but it does seem worthwhile to abstract them from the flux of life for purposes of analysis. In any case, that is what Piaget has done, and in his writing, "maturation" refers to genetic influences on development.
PHYSICAL EXPERIENCE
Interacting with the genetic effects is a factor called physical experience, which the child uses to abstract the various properties of physical objects. Whenever a child squeezes an object and finds it solid, drops it and discovers that it breaks, places it in water and watches it float, or has any other commerce with the object as object, he engages in an abstraction process that results in knowledge of that object and, ultimately, of the material
*The categories "physical experience" and "logico-mathematical experience" are often reduced to subcategories under the single category "experience." 12
of which the object is constituted. The experience is called physical to distinguish it from logico-mathematical experience, but paradoxically it always involves assimilation to logico-mathematical structures. The knowledge that a particular contour is horizontal, for example, depends upon the prior construction of a system of spatial coordinates. "Comparing two weights pressupposes the establishment of a relation, and therefore the construction of a logical form."13 Even the knowledge that a single object is "light" or "heavy" entails a comparison with some internalized standard and, again, presupposes the construction of a logical form.
LOGICO-MATHEMATICAL EXPERIENCE
It is in the nature of things for a child to act on the objects in his environment. When he does so, they "act back," so to speak, and the result is physical experience. But there is another kind of experience that comes when he constructs relationships among objects--or rather, among his actions on objects. Piaget relates a story told to him by a mathematician friend who at the age of four or five years
... was seated on the ground in his garden and he was counting pebbles. Now to count these pebbles he put them in a row and he counted them one, two, three, up to ten. Then he finished counting them and started to count them in the other direction. He began by the end and once again he found ten ... . There were ten in one direction and ten in the other direction. So he put them in a circle and counted them that way and found ten once again.14
What that child "learned" (in the broad sense) had to do not with the physical properties of the pebbles but with the relations among them. More precisely, what he accomplished was an organization of his actions with respect to the pebbles.
The concept of "ten"--and the quality of "tenness"--is not a property of pebbles but a construction of the child's mind. The experience of that construction, and of others similar to it, is called logico-mathematical to distinguish it from physical experience.
SOCIAL TRANSMISSSION
The knowledge that a child acquires from physical experience is abstracted from physical objects. In the case of logico-mathematical experience, knowledge is constructed from actions on objects. In social transmission, it comes from other people. They demonstrate, deliberately or otherwise, how things are done; they write things down in books; but mostly they just talk.
And some of their knowledge is acquired by the child. (Which knowledge, and under what conditions it is acquired, we shall discuss in the chapter on educational implications.) Acquisition of knowledge from another person is said to have occurred via social transmission.
EQUILIBRATION
Last, but definitely not least, is equilibration, which integrates the other four factors into itself. In fact, it is so much a part of them (and they of it) that I personally find it difficult to conceive of equilibration as a factor separate from the others. In any event, its special importance is implicit in the special treatment given to it in the previous section.

DEVELOPMENTAL UNITS
Piaget conceives of intellectual development as a continual process of organization and reorganization of structures, each new organization integrating the previous one into itself. Although that process is continuous, its results are discontinuous; they are qualitatively different from time to time. Because of that, Piaget has chosen to break the total course of development into units called periods and stages. Note carefully, however, that each of those cross sections of development is described in terms of the best the child can do at that time. Many previously acquired behaviors will occur even though he is capable of new and better ones.
Let us now examine the theory in detail, following the outline that appears in Table I. Then, having analyzed each unit in its turn, we'll look back and see whether it is possible to discern the unifying threads that run through all of them.
NOTES
1Jean Piaget and Alina Szeminska, The Child's Conception of Number, trans. C. Gattengno and F. M. Hodgson (New York: Humanities Press), 1952.
2Eleanor Duckworth, "Language and Thought," in Milton Schwebel and Jane Raph (eds.), Piaget in the Classroom (New York: Basic Books, Inc.), 1973, p. 149.
3Robert Rosenthal and K. L. Fade, "The Effect of Experimenter Bias on the Performance of the Albino Rat," Behavioral Science, 1963, pp. 183-189, and Robert Rosenthal and R. Lawson, "A Longitudinal Study of Experimenter Bias on the Operant Learning of Laboratory Rats," Journal of Psychiatric Research, 1964. An interesting study of the experimenter effect in humans is Robert Rosenthal and Lenore Jacobson, Pygmalion in the Classroom (New York: Holt, Rinehart and Winston, Inc.), 1968.
4My discussion has been significantly influenced by D. O. Hebb's analysis in his The Organization of Behavior (New York: John Wiley & Sons, Inc.), 1949 and in his A Textbook of Psychology (Philadelphia: W. B. Saunders), 1958.
5Jean Piaget, The Origins of Intelligence in Children, trans. Margaret Cook (New York: International Universities Press), 1952, p. 3.
6Ibid., p. 8.
7Loc. cit.
8T. G. R. Bower, "The Visual World of Infants," Scientific American, vol. 215, no. 6 (December 1966), pp. 80-92, and his "Phenomenal Identity and Form Perception in an Infant," Journal of Perception and Psychophysics, 1967, pp. 74-76.
9Jean Piaget, "Genetic Epistemology," Columbia Forum, Fall, 1969, p. 5.
10David Elkind (ed.), Six Psychological Studies (New York: Random House, Inc.), 1967, p. 109.
11Adapted from John H. Flavell's account in his The Developmental Psychology of Jean Piaget (Princeton: D. Van Nostrand Co., Inc.), 1963, pp. 215-249.
12Jean Piaget and Barbel Inhelder, The Psychology of the Child, trans. Helen Weaver (New York: Basic Books), 1969, pp. 155-156.
13Ibid., p. 155.
14Jean Piaget, "Development and Learning," in R. E. Ripple and V. N. Rockcastle (eds.), Piaget Rediscovered (Ithaca: Cornell Univ. Press), 1964. [Originally published as a section of Journal of Research in Science Teaching, vol. 2, 1964, p. 179.]


Copyright © 1969 and 1975 by W. H. Freeman and Company